A radiological dispersal device (RDD) is a device which spreads radioactive material over a wide area. There may be several forms of RDD, one being a dirty bomb which uses explosives to scatter radioactive material. Another type is an atmospheric device in which radioactive material is converted into a form that is transported by air currents. Radiological dispersal devices can result in human casualties by inhaling the radioactive material.
There are four primary entry routes of radionuclides into the body, including inhalation, ingestion, skin absorption and wound absorption. Once intaken (to the body), radionuclides must be uptaken (by cells) for any significant internal dose to be realized. The physiological retention and clearance of radionuclides is influenced by 1) mode of entry into the body, 2) radionuclide chemistry; 3) particle size of the radionuclide particles. Once uptaken, a radionuclide will irradiate surrounding tissues until it: 1) is excreted through physical processes (urine or feces), 2) is eliminated via radioactive decay, or 3) is removed via treatment (decorporation or wound debridement).
One of the greatest health risks from terrorist use of a radiological dispersal device (RDD) is from inhalation of radionuclide aerosol particulate after a high energy event (explosive, liquid or powder release). Although there are a number of strategies available to medically decorporate radionuclides from the body, their efficacy relies on the fact that they can be administered to patients rapidly (within hours) after the intake occurs. The appropriate therapeutic treatment regime depends primarily on the rapid identification of the radioisotope involved (for example, Cs-137, Co-60, Ir-192 etc).
The standard therapies for treatment include saturation of the target organ (ex. KI), complex formation at the site of entry or in body fluids followed by rapid excretion (ex. DTPA), acceleration of metabolic cycle of radionuclide by isotope dilution (ex. water), precipitation of radionuclide in intestinal lumen followed by faecal excretion (ex. BaSO4), ion exchange in gastrointestinal tract (ex. Prussian blue).
Of critical importance is the timing of the treatment so that administration of decorporating agents can be made as early as possible after uptake. In emergency situations where many people may be affected there is not generally sufficient time for detailed laboratory dose assessments prior to administering a standard protocol after intake. Currently, the decision to treat is therefore subjective and based upon experience, and therefore the risk is high that the assessment and treatment decisions may be wrong. Thus, first responders must weigh the small risk of the treatment against the potential aversion of dose. As discussed, treatment efficacy is highly dependent on time of treatment after insult. Also, it would be very desirable to rapidly clear people from the scene (mitigate “worried well” phenomena).
The first responders in such a scenario would be the nurses and doctors at the local hospital emergency rooms and the first people to arrive on the scene (firemen, police officers, EMT, etc) who typically would have little-to-no knowledge in health physics particularly as it relates to radiation hazards. The ability to treat is limited since the first responders own personal safety may be compromised. Common tools used by first responders in a radiation emergency are personal dosimeters and radiation survey meters.
Thus, unfortunately, first response personnel (EMS, fire fighters, police, nurses, etc) do not have the equipment and more importantly the expertise to perform rapid radionuclide assessment in the field. Therefore, by the time the isotopic contribution(s) is/are determined, the radionuclides will have been incorporated into intracellular fluids and are extremely difficult to remove from the body.
Operational experience has shown that personnel who have inhaled this type of material will have impaction transfer in the upper nasal-pharynx region, and therefore a positive indication from a filter-mask type device placed over the nose and mouth would be enough to indicate that decorporation for the specific radionuclide is recommended. It is believed that no such similar device currently exists and that this type of device, which would be simple enough such that minimally trained non-experts could use it, would be an immediately realizable asset to first responders that may be called upon to provide medical assistance after an RDD scenario.
From a medical perspective, the biggest challenge for the treating physicians is: 1) finding out what radioisotope is involved, and then, 2) whether the exposure is great enough to warrant treatment. Early treatment is essential for maximizing the potential of the drugs involved.
It would be very advantageous to provide radiation detection devices for rapid triage of personnel at risk of internal radionuclide contamination from inhalation.